Unfortunately, they are correct when they said it cannot. Time Machine does a good job of backing up all the files that are on your Mac HD but that is all. It is not a backup software that can select drives to clone or anything like that. It keeps a persistent backup of everything you store on your Mac HD and that is all. Here's a link to the actual Mac 101 about it. Mac 101: Time Machine Having said that, you can find other software out there that will allow you to select network drives and back up their data to another source. I personally use backuplist+ to get the job done for either backing up to a network drive or from the drive ( You can select any drive available to backup to any other drive) Its a powerful little tool good developer support. There are probably other options as well out there. I would recommend though partitioning the Time Capsule drive for the area where you will store the backup of the WD just to wall it off from interfering with the Time Machine backup (not that it would but just to be safe)